This invention relates to multi-speed power transmissions and more particularly to such transmissions having a plurality of planetary gear sets.
Passenger vehicles, cars and trucks, have a powertrain most of which include a multi-speed planetary transmission. The transmission may be of either the countershaft type or the planetary gear type. The planetary gear type of transmissions are provided with controls to automatically change the gear ratios in the transmission as the vehicle is moving. To provide good performance, the transmission has two or more gear sets that are interconnected and a plurality of torque transmitting mechanisms, clutches and brakes, to control the operating ratios of the transmission.
The transmission generally has three or more forward speed ratios, a reverse drive ratio and a neutral condition. As the number of forward drive ratios increases, the number of gear sets and torque transmitting mechanisms increases. However, transmissions are known to provide six forward speed ratios, and a reverse ratio from three planetary gear sets and a minimum of five torque transmitting mechanisms. Also, it is possible to provide an input planetary, chain drive, or countershaft gear set that is dedicated to provide both a direct drive input and a ratio drive input to a multi-speed planetary gear arrangement. The ratio drive input can be greater than unity or less than unity thereby increasing the number of speeds available from the planetary gear arrangement. In many off-road type vehicles and hauling vehicles, this additional input gear set is termed a xe2x80x98splitterxe2x80x99. The additional gear set can have a torque transmitting mechanism to establish the ratio drive input or it can operate to continuously provide torque to both input ratios.
It is an object of the present invention to provide an improved multi-speed transmission.
In one aspect of the present invention, an input gear set provides a direct drive and an underdrive to a plurality of selectively engageable torque transmitting mechanisms. In another aspect of the present invention, a pair of interconnected planetary gear sets are selectively connectable with the input gear set through the torque transmitting mechanisms. In yet another aspect of the present invention, at least one additional torque transmitting mechanism is selectively connectable with one member of the planetary gear sets.
In still another aspect of the present invention, the judicious selection of the torque transmitting mechanisms provides seven or eight forward speed ratios. In yet still another aspect of the present invention, the planetary gear sets have a torque transmitting mechanism selectively connectable with one member. In a further aspect of the present invention, one embodiment thereof is controlled to provide two reverse drive ratios and a minimum of seven ratios. In a yet further aspect of the present invention, the seven or eight forward drive ratios and one reverse drive ratio are attained with a minimum of five torque transmitting mechanisms. In a still further aspect of the present invention, eight forward drive ratios and two reverse drive ratios are attained with six torque transmitting mechanisms. In a yet still further aspect of the present invention, four of the torque transmitting mechanisms are rotating torque transmitting mechanisms and the remaining torque transmitting mechanisms are stationary torque transmitting mechanisms.